The advent of Micro Inverters - Scourge or Saviour?

Any new technology comes about for good reasons - folk won't buy if it does not deliver.

The question of concern here is - will it deliver for our market, and the signs we've seen so far give us doubts. Now that's not to say that these doubts can't be cleared up, its just that we are not getting the answers we would have thought.

There are definite advantages with the concept of using a micro-inverter (and indeed an 'optimiser') per panel. Briefly:

Each panel in effect operates independently - its operation does not affect the operation of any other panel. It means that one panel can be shaded, or face another direction, and the others are not affected. Variations in panel performance due to manufacturing variation are not an issue.

Each panel/inverter can be monitored for yield and any errors should they occur.

Disadvantages are:

Micro inverter systems are at this time considerably more expensive than a conventional 'string'-inverter system.

Micro systems in Australia do not appear to yield the extra power claimed by many marketers (unless you have significant shading or other factors)

Servicing costs are higher - think of a serviceperson climbing your roof to replace a micro

These are the questions given to various manufacturers, but yet without a suitable answer:

Please provide a thermal photograph of an array at 45°C ambient on a sunny day. Object being to see what temperature differences/gradients is/are shown across the faces of panels with micros underneath (best we've received so far is one at 25°C - doesn't count in Australia!).

Does this indicate an ambient air temperature under the panel in excess of 65°C? - which is the datasheet limit for most brands.

If the ambient datasheet ambient temperature limit is exceeded, what guarantee does the customer have that the manufacturer will honour the warranty? Because legally it looks as if they do not have to! (one manufacturer indicated 79°C was recorded inside one of their micros one day in Jan 2014 - they are the exception in that that their datasheet limit goes to 85°C)

Do any manufacturer warranties for micros provide any part or full funding for the labour to climb on the roof and exchange any failing micro? Otherwise of course it is an additional risk to cost of ownership for micro customers. (one manufacturer indicates they do)

Please provide comparative annual data for a micro array in Australia? (still waiting for a full years results across numerous sites)

This last point should be a no-brainer, and yet I often hear gains of “25%” over string inverters arbitrarily quoted in the market place, but with no apparent data reference, and certainly not one applicable to Australia.

The temperatures encountered under the array can be extreme. We have seen plastic conduit carrying cable soften, deform and pull out of its (glued) sockets due extremes of temperature. Now I must add that there were a couple of extra factors at play here - the conduit was placed at the very top of the array, and the roof design did not allow quite as much ventilation as normal. But then, many of the 'AC panels', which are panels that have micros mounted on them, have those micros (that get hot) mounted very close to the backing sheet plastic ('tedlar') - just as close as our example plastic conduit that deformed! (manufacturer's may specify a minimum distance from roof-to-micro and from micro-to-panel backsheet)

Now I must stress that this really may not be an issue - if the manufacturers can provide comprehensive data of actual temperatures. We're still waiting....

Now we know that micros have been installed in Australia for at least a few years, but, surely as a customer, we would want and expect the micro system to last for 25 to 30 years or more. And most, or even some, brands and models may well do that.

But as a supplier of solar equipment, we are putting our time, money and commitment on the line for any product we sell. Failures under warranty are rarely ever a break-even affair for the installation business - warranty costs are at best only partly recoverable by whoever does the warranty work.

Unfortunately, we have heard that there have been, and still are, businesses out there that operate on the concept of sell, sell, while the goings good, then close the doors, disappear, de-register or whatever, if ever a *major* warranty event occurs. This is where the cost of administering a wide-ranging warranty 'event' is just too great, so the business goes bust instead (think of a recall of thousands of items).

We believe, at this stage, the average micro is too great a gamble for longevity, given the reticence of manufacturers to 'talk Australian temperatures' under the array on one of our roofs in high-summer.

Chris Hart has been employed in the field of IT majoring in hardware and power issues for over 20 years, followed by 15 years designing and supplying solar battery systems for domestic and commercial markets. He has qualifications in electronic engineering and management.